The hippocampus, located on either side of the center of the brain, is responsible for the consolidation of short term memories into long term memories. It is also responsible for spatial navigation.
Alzheimer’s disease impacts the hippocampus causing it’s volume to contract significantly over time. Given that those with Alzheimer’s disease lose their memory and are often disoriented, it is or “was” natural to conclude that the reduced size of the hippocampus was a physical manifestation of deteriorating memory.
It is also known that marijuana and nicotine by themselves cause the hippocampus’ volume to contract. Therefore, the combination of nicotine and marijuana should be even more harmful to the hippocampus and therefore, memory function, right???
Dr. Francesca Filbey and her colleagues at the Center for Brain Health in Dallas conducted and released a study on the combined use of these substances:
The findings were that, among participants who used both marijuana and nicotine, the smaller their hippocampus, the better their memory compared to others with a bigger hippocampus who also used both. And those that smoked the most tobacco had the smallest hippocampus but best memory compared to the others. The same was observed to a lesser degree among those who solely used marijuana or tobacco.
“That’s the surprising effect we found,” lead researcher Francesca Filbey told IFLScience. “It’s not what we expected.”
It is important to note that this research study only looked at short term memory and that there was not a significant difference in the memory results among the participants in the study.
While much more research needs to be done in order to understand the interplay of nicotine and marijuana, the encouraging news is that there may be more mechanisms and/or structures at play in memory than hippocampal volume.